Selection of cattle with greater feed efficiency is known to be profitable. Savings in southern Australian beef production systems of $6.55 per breeding cow per year have been estimated for selection for lower residual feed intake (RFI), and an additional saving of $4.34 per breeding cow per year may be achieved in feedlots. Greater feed efficiency is also expected to reduce methane emissions. A gene flow model was developed to simulate the spread of improved RFI genes through both a single herd in southern Australia and in the national herd, from 2002 to 2026. Based on the estimated gene flow, voluntary feed intakes were revised annually, and changes in subsequent methane emissions were calculated for both the individual and national herd. The annual methane emissions in year 25 of selection were 15.9% less than in year one for an adopting herd. For the national herd, given differential lags in and limits to adoption for Northern and Southern Australia, the cumulative reduction in national emissions was 568.1 Gg of methane over 25 years (11.93 Mt CO2 equivalents), with annual emissions in year 25 being 3.1% lower than in year 1. It is concluded that selection for reduced RFI will lead to substantial and lasting methane abatement while also providing savings in feed-related costs for Australian beef producers, largely as a consequence of its implementation as a breeding objective for the beef herd.